1. Field of the Invention
The present invention relates to an oxygen gas production apparatus which provides high purity gaseous oxygen in pressurized state.
2. Description of the Prior Art
It is customary to produce oxygen gas in an air fractionation plant which separates oxygen from nitrogen by taking advantage of their difference in boiling point. This conventional air fractionation plant is provided with an expansion turbine for generating the refrigeration necessary for the liquefaction and fractionation of air, which utilizes the "cold heat" due to adiabatic expansion.
However, because of its extremely high speed (tens of thousand revolutions per minute), the expansion turbine cannot delicately follow variations in load (variations in the rate of withdrawal of product oxygen gas). Thus, it is technically difficult to vary the rotational speed of the expansion turbine quickly and accurately in response to changes in the amount of withdrawal of product oxygen gas so as to maintain the compressed material air at a constant temperature at all times. As a result, a variation is inevitable in the purity of product oxygen gas, for low purity oxygen is frequently output to depress the overall purity of product oxygen. Furthermore, because it is driven at a very high speed, the expansion turbine demands high mechanical precision and is costly to manufacture. In addition, its complicated structure calls for specially trained maintenance personnel. These problems emanate generally from the high-speed-revolving component of the expansion turbine and there has been a strong demand for elimination of an expansion turbine having such a high-speed revolving element from the oxygen production installation.
While product gaseous oxygen is sent to points of consumption via the product oxygen gas withdrawal line of the air fractionation plant, this transport is smoothly carried out when the pressure of product oxygen gas is high. Moreover, pressurized product oxygen gas is more convenient for consumption.
Accomplished in view of the above state of the art, the present invention is directed to:
(1) an oxygen gas production apparatus comprising an air compression means for compressing air from an outside source, a purification means for removing carbon dioxide gas and water vapor from the air compressed by said air compression means, a heat exchange means for chilling the compressed air from said purification means to a cryogenic temperature, a fractionation column for liquefying and fractionating the compressed air chilled to a cryogenic temperature by said heat exchange means and holding nitrogen in gaseous state and oxygen in liquid state, a liquid oxygen storage means for receiving liquid oxygen from an outside source and storing the same, a line for continuously introducing into said fractionation column the liquid oxygen from said liquid oxygen storage means in lieu of the generated refrigeration from a cold heat generating expansion means, an oxygen gas withdrawal line for guiding the liquid oxygen within said fractionation column as a refrigerant to said heat exchange means and withdrawing the gasified oxygen produced by heat exchange as a product oxygen gas, and a pressurizing means for pressurizing the product oxygen gas withdrawn from said oxygen withdrawal line; and PA0 (2) an oxygen gas production apparatus comprising an air compression means for compressing air from an outside source, a purification means for removing carbon dioxide gas and water vapor from the air compressed by said air compression means, a heat exchange means for chilling the compressed air from said purification means to a cryogenic temperature, a fractionation column for liquefying and fractionating the compressed air chilled to a cryogenic temperature by said heat exchange means and holding nitrogen in gaseous state and oxygen in liquid state, a liquid oxygen storage means for receiving liquid oxygen from an outside source and storing the same, a line for continuously introducing into said fractionation column the liquid oxygen from said liquid oxygen storage means in lieu of the generated refrigeration from a cold heat generating expansion means, a liquid oxygen withdrawal line for withdrawing liquid oxygen from said fractionation column, a pressurizing means for pressurizing the liquid oxygen from said liquid oxygen withdrawal line, and an oxygen gas withdrawal line for guiding the liquid oxygen pressurized by said pressurizing means to said heat exchange means as a refrigerant and withdrawing the gasified oxygen produced by heat exchange as a product oxygen gas.
The advantages of the oxygen gas production apparatus according to the present invention include the following. Firstly, because it does not include an expansion turbine but, instead, uses a liquid oxygen storage means, such as a liquid oxygen storage tank, which has no revolving part, the whole equipment is virtually free of operation troubles and failures. Moreover, whereas the expansion turbine is an expensive machine, the liquid oxygen storage tank is available at low cost and does not call for special maintenance personnel. The expansion turbine is further disadvantageous in that since it cannot be easily driven to follow variations in load faithfully, i.e. at a varying rotational speed commensurate with the varying rate of withdrawal of product oxygen gas, the compressed air cannot be chilled to a predetermined temperature at all times. In contrast, the apparatus according to the present invention includes a liquid oxygen storage means in lieu of an expansion turbine and uses liquid oxygen which can be supplied at delicately controlled rates as a refrigeration medium so that product oxygen gas of very high purity can be obtained on a constant basis. In addition, because this apparatus is provided with a pressurizing means, the high-purity product oxygen can be made available in pressurized condition which is convenient in use at points of consumption. Particularly, the above principle of pressurizing liquid oxygen results in a remarkable improvement in the efficiency of compression, leading to drastic reductions in oxygen gas production cost and equipment scale. Moreover, since a liquid can be more easily compressed than a gas, the required seal may be less positive, so that it is easier to prevent oxygen leaks. In other words, the leakage of oxygen can be completely inhibited. Therefore, the present invention is a remarkable step forward from the standpoint of prevention of explosion and other hazards as well.